1. Field of the Invention
The present invention relates to an internal-surface-scanning image recording apparatus for recording an image on a photosensitive medium held against the cylindrical inner circumferential surface of a support, by scanning the photosensitive medium with a light beam that has been modulated with image information.
2. Description of the Related Art
Apparatus for recording an image on a photosensitive medium with a laser beam include a planar-surface-scanning image recording apparatus for applying a laser beam in a main scanning direction to a planar photosensitive medium which is being fed in an auxiliary scanning direction to record an image on the planar photosensitive medium, an external-surface-scanning image recording apparatus for applying a laser beam to a photosensitive medium mounted on the outer circumferential surface of a drum which is being rotated to record an image on the photosensitive medium, and an internal-surface-scanning image recording apparatus for applying a laser beam to a photosensitive medium mounted on the cylindrical inner circumferential surface of a support drum to record an image on the photosensitive medium.
The internal-surface-scanning image recording apparatus is in widespread usage because the photosensitive medium is fixedly mounted on the semicylindrical inner circumferential surface of the support, and the image is recorded by rotating an exposure head for emitting the laser beam about the central axis of the semicylindrical inner circumferential surface, so that the photosensitive medium is prevented from being peeled off during the recording process, the recorded image has high dimensional accuracy, and the apparatus is capable of high-speed scanning and is highly economical.
FIGS. 1 and 2 of the accompanying drawings schematically show a conventional internal-surface-scanning image recording apparatus 2. As shown in FIGS. 1 and 2, the conventional internal-surface-scanning image recording apparatus 2 has a support 6 with a photosensitive medium S mounted on a semicylindrical inner circumferential surface 4 thereof, and a recording unit 8 for applying a laser beam L modulated with image information to the photosensitive medium S to record an image thereon.
The recording unit 8 has an arm 12 whose opposite ends movably engage in respective guide grooves 10a, 10b defined in the support 6 for movement in the auxiliary scanning direction indicated by the arrow Y. The recording unit 8 has an exposure head 14 housed therein for emitting a laser beam L. To the exposure head 14, there is connected a light source 16 for supplying the laser beam L that has been modulated with image information to the exposure head 14. The exposure head 14 and the light source 16 are movable about the central axis of the semicylindrical inner circumferential surface 4 for thereby scanning the photosensitive medium S with the laser beam L in the main scanning direction indicated by the arrow X.
In the conventional internal-surface-scanning image recording apparatus 2, because the image is recorded on the photosensitive medium S only when the exposure head 14 that outputs the laser beam L faces the photosensitive medium S, the laser beam L which is outputted by the exposure head 14 when the exposure head 14 does not face the photosensitive medium S is wasted. The conventional internal-surface-scanning image recording apparatus 2 cannot record the image at a high speed because the photosensitive medium S is scanned only in one cycle while the exposure head 14 makes one revolution if a single laser beam L is outputted from the exposure head 14.
The above drawbacks may be overcome by using a support 6 having a nearly fully cylindrical inner circumferential surface 4 to utilize the laser beam L effectively for increased recording efficiency. However, such a structure would make it difficult to attach the photosensitive medium S to and remove the photosensitive medium S from the support 6. Particularly, if an image is to be recorded on a printing plate, then the photosensitive medium S which is highly rigid needs to be curved to a large curvature, and may possibly be damaged when it is curved. Therefore, it is a time-consuming process to attach the photosensitive medium S to and remove the photosensitive medium S from the support, with the result that high-speed image recording cycles cannot be achieved.
High-speed image recording may be performed by increasing the speed at which the exposure head 14 rotates. When the exposure head 14 rotates at a high speed, it tends to suffer rotational speed irregularities, and it is liable to produce noise and heat.